Variable capacity furnace

ABSTRACT

A furnace for a heating, ventilation, and air conditioning (HVAC) system includes a fuel valve configured to regulate an amount of fuel supplied to a burner of the furnace, a draft inducer blower configured to draw an air flow into the burner, and a controller configured to determine a target operating parameter value of the furnace, determine an air to fuel ratio corresponding to the target operating parameter value, and control operation of the fuel valve, the draft inducer blower, or both based on the air to fuel ratio.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from and the benefit of U.S. Provisional Application No. 63/303,889, entitled “FURNACE,” filed Jan. 27, 2022, which is hereby incorporated by reference in its entirety for all purposes.

BACKGROUND

This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.

Heating, ventilation, and air conditioning (HVAC) systems are utilized in residential, commercial, and industrial environments to control environmental properties, such as temperature, humidity, and/or air quality, for occupants of the respective environments. The HVAC system may regulate the environmental properties through delivery of a conditioned air flow to the environment. For example, the HVAC system may include a furnace system that is used to heat an air flow supplied to an air distribution system of the building. Such furnace systems may typically include a burner assembly and a heat exchanger that cooperate to produce heated supply air, which may be directed through the air distribution system to heat a room or other space within the building. Unfortunately, conventional furnace systems may be unable or ill-equipped to effectively regulate generation and/or output of the heated supply air in an efficient manner to achieve desired climate parameters in the room or other space serviced by the HVAC system.

SUMMARY

A summary of certain embodiments disclosed herein is set forth below. It should be noted that these aspects are presented merely to provide the reader with a brief summary of these certain embodiments and that these aspects are not intended to limit the scope of this disclosure. Indeed, this disclosure may encompass a variety of aspects that may not be set forth below.

The present disclosure relates to a furnace for a heating, ventilation, and air conditioning (HVAC) system including a fuel valve configured to regulate an amount of fuel supplied to a burner of the furnace, a draft inducer blower configured to draw an air flow into the burner, and a controller configured to determine a target operating parameter value of the furnace, determine an air to fuel ratio corresponding to the target operating parameter value, and control operation of the fuel valve, the draft inducer blower, or both based on the air to fuel ratio.

The present disclosure also relates to a furnace controller for a furnace of a heating, ventilation, and air conditioning (HVAC) system including processing circuitry and a memory. The memory includes instructions that, when executed by the processing circuitry, cause the processing circuitry to determine a target firing rate of the furnace, determine an air to fuel ratio of a plurality of air to fuel ratios corresponding to the target firing rate, and control operation of a fuel valve of the furnace, a draft inducer blower of the furnace, or both based on the air to fuel ratio.

The present disclosure further relates to a furnace for a heating, ventilation, and air conditioning (HVAC) system including a burner configured to receive a flow of fuel and an air flow, to mix the flow of fuel and the air flow produce an air-fuel mixture, and to ignite the air-fuel mixture to generate combustion products. The furnace also includes a heat exchanger system configured to receive the combustion products and direct the combustion products therethrough and a controller including a memory. The controller is configured to determine a target operating parameter value of the furnace based on data received by the controller, select an air to fuel ratio of a plurality of air to fuel ratios stored on the memory, where the air to fuel ratio corresponds to the target operating parameter value, and control operation of the furnace to produce the air-fuel mixture with the air to fuel ratio.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of this disclosure may be better understood upon reading the following detailed description and upon reference to the drawings in which:

FIG. 1 is a perspective view of an embodiment of a building incorporating a heating, ventilation, and air conditioning (HVAC) system in a commercial setting, in accordance with an aspect of the present disclosure;

FIG. 2 is a perspective view of an embodiment of a packaged HVAC unit, in accordance with an aspect of the present disclosure;

FIG. 3 is a cutaway perspective view of an embodiment of a split, residential HVAC system, in accordance with an aspect of the present disclosure;

FIG. 4 is a schematic diagram of an embodiment of a vapor compression system used in an HVAC system, in accordance with an aspect of the present disclosure;

FIG. 5 is a cutaway perspective view of an embodiment of a portion of an HVAC system having a furnace system, in accordance with an aspect of the present disclosure; and

FIG. 6 is a schematic of an embodiment of a furnace system, in accordance with an aspect of the present disclosure.

DETAILED DESCRIPTION

One or more specific embodiments of the present disclosure will be described below. These described embodiments are examples of the presently disclosed techniques. Additionally, in an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.

When introducing elements of various embodiments of the present disclosure, the articles “a,” “an,” and “the” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Additionally, it should be understood that references to “one embodiment” or “an embodiment” of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features.

As used herein, the terms “approximately,” “generally,” and “substantially,” and so forth, are intended to convey that the property value being described may be within a relatively small range of the property value, as those of ordinary skill would understand. For example, when a property value is described as being “approximately” equal to (or, for example, “substantially similar” to) a given value, this is intended to mean that the property value may be within +/−5%, within +/−4%, within +/−3%, within +/−2%, within +/−1%, or even closer, of the given value. Similarly, when a given feature is described as being “substantially parallel” to another feature, “generally perpendicular” to another feature, and so forth, this is intended to mean that the given feature is within +/−5%, within +/−4%, within +/−3%, within +/−2%, within +/−1%, or even closer, to having the described nature, such as being parallel to another feature, being perpendicular to another feature, and so forth. Further, it should be understood that mathematical terms, such as “planar,” “slope,” “perpendicular,” “parallel,” and so forth are intended to encompass features of surfaces or elements as understood to one of ordinary skill in the relevant art, and should not be rigidly interpreted as might be understood in the mathematical arts. For example, a “planar” surface is intended to encompass a surface that is machined, molded, or otherwise formed to be substantially flat or smooth (within related tolerances) using techniques and tools available to one of ordinary skill in the art. Similarly, a surface having a “slope” is intended to encompass a surface that is machined, molded, or otherwise formed to be oriented at an angle (e.g., incline) with respect to a point of reference using techniques and tools available to one of ordinary skill in the art.

As briefly discussed above, a heating, ventilation, and/or air conditioning (HVAC) system may be used to thermally regulate a space within a building, home, or other suitable structure. For example, the HVAC system may include a furnace system that enables the HVAC system to supply heated air to rooms or zones within a building or other suitable structure serviced by the HVAC system. Typical furnace systems include one or more burner assemblies and a heat exchanger that cooperate to produce the heated supply air. For example, furnace systems may operate by burning or combusting a mixture of air and fuel in the burner assemblies to produce hot combustion products that are directed through tubes or piping of the heat exchanger. A blower may direct an air flow across the tubes or piping of the heat exchanger, thereby enabling the air flow to absorb thermal energy from the combustion products. In this manner, heated supply air may be produced and discharged from the furnace system and then directed to the rooms or zones of the building. For example, the blower may direct the heated supply air through an air distribution system of the building, such as through a system of ductwork and/or suitable conduits, and thereby supply the heated air to rooms or zones of the building in response to a call for heating.

In some applications, the furnace system may be a variable capacity furnace system. For example, a valve configured to control flow of fuel to a burner of the furnace system may be adjusted to modify a flow rate of fuel to the burner for combustion. The valve may be a modulating valve or other variable valve configured to be adjusted between a lower threshold valve position, an upper threshold valve position, and a plurality of valve positions therebetween. The position of the valve may be selected based on one or more operating parameters of the furnace system and/or HVAC system having the furnace system. For example, the position of the valve may be selected based on a difference between a temperature of return air received by the furnace system and a desired temperature (e.g., set point temperature) of a space serviced by the furnace system. As discussed herein, a position of the valve (e.g., an amount or percentage in which the valve is open) may be referred to as a “firing rate” of the furnace system. Thus, a variable capacity furnace system may be configured to operate at a plurality of firing rates (e.g., a plurality of valve positions) or operating capacities.

The furnace system may also include a draft inducer blower (e.g., draft inducer fan, draft inducer) configured to draw air into the tubes or pipes of the heat exchanger of the furnace system, which is mixed with the fuel and is combusted to generate the combustion products. As will be appreciated, the air-fuel mixture generated by the furnace system may have an air to fuel ratio (e.g., an amount or mass of air relative to an amount or mass of fuel within the air-fuel mixture). Unfortunately, existing furnace systems operate to generate air-fuel mixtures with constant air to fuel ratios irrespective of a firing rate or valve position with which the furnace system is operated.

It is now recognized that a constant air to fuel ratio may enable acceptable operation of the furnace system at some firing rates (e.g., fuel valve positions) but may not enable desirable operation of the furnace system at other firing rates (e.g., fuel valve positions). Indeed, implementation of a constant air to fuel ratio may result in inefficient operation of the furnace system at certain firing rates or ranges of firing rates. Accordingly, embodiments of the present disclosure are directed to furnace systems configured to operate with variable air to fuel ratios. For example, present embodiments include furnace systems configured to determine a desired air to fuel ratio for each firing rate (e.g., valve position) of a plurality of firing rates at which the furnace system may be operated. Based on a determined air to fuel ratio for a particular firing rate of the furnace system, the furnace system may be operated to achieve the desired air to fuel ratio. In this way, furnace systems incorporating the present techniques may operate more efficiently and more reliably across a wider range of firing rates (e.g., valve positions, operating capacities). Indeed, embodiments incorporating the present techniques may enable operation of variable capacity furnace systems with reduced emissions. These and other features will be described below with reference to the drawings.

Turning now to the drawings, FIG. 1 illustrates an embodiment of a heating, ventilation, and/or air conditioning (HVAC) system for environmental management that employs one or more HVAC units in accordance with the present disclosure. As used herein, an HVAC system includes any number of components configured to enable regulation of parameters related to climate characteristics, such as temperature, humidity, air flow, pressure, air quality, and so forth. For example, an “HVAC system” as used herein is defined as conventionally understood and as further described herein. Components or parts of an “HVAC system” may include, but are not limited to, all, some of, or individual parts such as a heat exchanger, a heater, an air flow control device, such as a fan, a sensor configured to detect a climate characteristic or operating parameter, a filter, a control device configured to regulate operation of an HVAC system component, a component configured to enable regulation of climate characteristics, or a combination thereof. An “HVAC system” is a system configured to provide such functions as heating, cooling, ventilation, dehumidification, pressurization, refrigeration, filtration, or any combination thereof. The embodiments described herein may be utilized in a variety of applications to control climate characteristics, such as residential, commercial, industrial, transportation, or other applications where climate control is desired.

In the illustrated embodiment, a building 10 is air conditioned by a system that includes an HVAC unit 12 with a reheat system in accordance with present embodiments. The building 10 may be a commercial structure or a residential structure. As shown, the HVAC unit 12 is disposed on the roof of the building 10; however, the HVAC unit 12 may be located in other equipment rooms or areas adjacent the building 10. The HVAC unit 12 may be a single package unit containing other equipment, such as a blower, integrated air handler, and/or auxiliary heating unit. In other embodiments, the HVAC unit 12 may be part of a split HVAC system, such as the system shown in FIG. 3 , which includes an outdoor HVAC unit 58 and an indoor HVAC unit 56.

The HVAC unit 12 is an air-cooled device that implements a refrigeration cycle to provide conditioned air to the building 10. Specifically, the HVAC unit 12 may include one or more heat exchangers across which an air flow is passed to condition the air flow before the air flow is supplied to the building. In the illustrated embodiment, the HVAC unit 12 is a rooftop unit (RTU) that conditions a supply air stream, such as environmental air and/or a return air flow from the building 10. After the HVAC unit 12 conditions the air, the air is supplied to the building 10 via ductwork 14 extending throughout the building 10 from the HVAC unit 12. For example, the ductwork 14 may extend to various individual floors or other sections of the building 10. In certain embodiments, the HVAC unit 12 may be a heat pump that provides both heating and cooling to the building with one refrigeration circuit configured to operate in different modes. In other embodiments, the HVAC unit 12 may include one or more refrigeration circuits for cooling an air stream and a furnace for heating the air stream.

A control device 16, one type of which may be a thermostat, may be used to designate the temperature of the conditioned air. The control device 16 also may be used to control the flow of air through the ductwork 14. For example, the control device 16 may be used to regulate operation of one or more components of the HVAC unit 12 or other components, such as dampers and fans, within the building 10 that may control flow of air through and/or from the ductwork 14. In some embodiments, other devices may be included in the system, such as pressure and/or temperature transducers or switches that sense the temperatures and pressures of the supply air, return air, and so forth. Moreover, the control device 16 may include computer systems that are integrated with or separate from other building control or monitoring systems, and even systems that are remote from the building 10.

FIG. 2 is a perspective view of an embodiment of the HVAC unit 12. In the illustrated embodiment, the HVAC unit 12 is a single package unit that may include one or more independent refrigeration circuits and components that are tested, charged, wired, piped, and ready for installation. The HVAC unit 12 may provide a variety of heating and/or cooling functions, such as cooling only, heating only, cooling with electric heat, cooling with dehumidification, cooling with gas heat, or cooling with a heat pump. As described above, the HVAC unit 12 may directly cool and/or heat an air stream provided to the building 10 to condition a space in the building 10.

As shown in the illustrated embodiment of FIG. 2 , a cabinet 24 encloses the HVAC unit 12 and provides structural support and protection to the internal components from environmental and other contaminants. In some embodiments, the cabinet 24 may be constructed of galvanized steel and insulated with aluminum foil faced insulation. Rails 26 may be joined to the bottom perimeter of the cabinet 24 and provide a foundation for the HVAC unit 12. In certain embodiments, the rails 26 may provide access for a forklift and/or overhead rigging to facilitate installation and/or removal of the HVAC unit 12. In some embodiments, the rails 26 may fit into “curbs” on the roof to enable the HVAC unit 12 to provide air to the ductwork 14 from the bottom of the HVAC unit 12 while blocking elements such as rain from leaking into the building 10.

The HVAC unit 12 includes heat exchangers 28 and 30 in fluid communication with one or more refrigeration circuits. Tubes within the heat exchangers 28 and 30 may circulate refrigerant, such as R-410A, through the heat exchangers 28 and 30. The tubes may be of various types, such as multichannel tubes, conventional copper or aluminum tubing, and so forth. Together, the heat exchangers 28 and 30 may implement a thermal cycle in which the refrigerant undergoes phase changes and/or temperature changes as it flows through the heat exchangers 28 and 30 to produce heated and/or cooled air. For example, the heat exchanger 28 may function as a condenser where heat is released from the refrigerant to ambient air, and the heat exchanger 30 may function as an evaporator where the refrigerant absorbs heat to cool an air stream. In other embodiments, the HVAC unit 12 may operate in a heat pump mode where the roles of the heat exchangers 28 and 30 may be reversed. That is, the heat exchanger 28 may function as an evaporator and the heat exchanger 30 may function as a condenser. In further embodiments, the HVAC unit 12 may include a furnace for heating the air stream that is supplied to the building 10. While the illustrated embodiment of FIG. 2 shows the HVAC unit 12 having two of the heat exchangers 28 and 30, in other embodiments, the HVAC unit 12 may include one heat exchanger or more than two heat exchangers.

The heat exchanger 30 is located within a compartment 31 that separates the heat exchanger 30 from the heat exchanger 28. Fans 32 draw air from the environment through the heat exchanger 28. Air may be heated and/or cooled as the air flows through the heat exchanger 28 before being released back to the environment surrounding the HVAC unit 12. A blower assembly 34, powered by a motor 36, draws air through the heat exchanger 30 to heat or cool the air. The heated or cooled air may be directed to the building 10 by the ductwork 14, which may be connected to the HVAC unit 12. Before flowing through the heat exchanger 30, the conditioned air flows through one or more filters 38 that may remove particulates and contaminants from the air. In certain embodiments, the filters 38 may be disposed on the air intake side of the heat exchanger 30 to prevent contaminants from contacting the heat exchanger 30.

The HVAC unit 12 also may include other equipment for implementing the thermal cycle. Compressors 42 increase the pressure and temperature of the refrigerant before the refrigerant enters the heat exchanger 28. The compressors 42 may be any suitable type of compressors, such as scroll compressors, rotary compressors, screw compressors, or reciprocating compressors. In some embodiments, the compressors 42 may include a pair of hermetic direct drive compressors arranged in a dual stage configuration 44. However, in other embodiments, any number of the compressors 42 may be provided to achieve various stages of heating and/or cooling. As may be appreciated, additional equipment and devices may be included in the HVAC unit 12, such as a solid-core filter drier, a drain pan, a disconnect switch, an economizer, pressure switches, phase monitors, and humidity sensors, among other things.

The HVAC unit 12 may receive power through a terminal block 46. For example, a high voltage power source may be connected to the terminal block 46 to power the equipment. The operation of the HVAC unit 12 may be governed or regulated by a control board 48. The control board 48 may include control circuitry connected to a thermostat, sensors, and alarms. One or more of these components may be referred to herein separately or collectively as the control device 16. The control circuitry may be configured to control operation of the equipment, provide alarms, and monitor safety switches. Wiring 49 may connect the control board 48 and the terminal block 46 to the equipment of the HVAC unit 12.

FIG. 3 is a cutaway perspective view of a residential heating and cooling system 50, also in accordance with present techniques. The residential heating and cooling system 50 may provide heated and cooled air to a residential structure, as well as provide outside air for ventilation and provide improved indoor air quality (IAQ) through devices such as ultraviolet lights and air filters. In the illustrated embodiment, the residential heating and cooling system 50 is a split HVAC system. In general, a residence 52 conditioned by a split HVAC system may include refrigerant conduits 54 that operatively couple the indoor unit 56 to the outdoor unit 58. The indoor unit 56 may be positioned in a utility room, an attic, a basement, and so forth. The outdoor unit 58 is typically situated adjacent to a side of residence 52 and is covered by a shroud to protect the system components and to prevent leaves and other debris or contaminants from entering the unit. The refrigerant conduits 54 transfer refrigerant between the indoor unit 56 and the outdoor unit 58, typically transferring primarily liquid refrigerant in one direction and primarily vaporized refrigerant in an opposite direction.

When the system shown in FIG. 3 is operating as an air conditioner, a heat exchanger 60 in the outdoor unit 58 serves as a condenser for re-condensing vaporized refrigerant flowing from the indoor unit 56 to the outdoor unit 58 via one of the refrigerant conduits 54. In these applications, a heat exchanger 62 of the indoor unit functions as an evaporator. Specifically, the heat exchanger 62 receives liquid refrigerant, which may be expanded by an expansion device, and evaporates the refrigerant before returning it to the outdoor unit 58.

The outdoor unit 58 draws environmental air through the heat exchanger 60 using a fan 64 and expels the air above the outdoor unit 58. When operating as an air conditioner, the air is heated by the heat exchanger 60 within the outdoor unit 58 and exits the unit at a temperature higher than it entered. The indoor unit 56 includes a blower or fan 66 that directs air through or across the indoor heat exchanger 62, where the air is cooled when the system is operating in air conditioning mode. Thereafter, the air is passed through ductwork 68 that directs the air to the residence 52. The overall system operates to maintain a desired temperature as set by a system controller. When the temperature sensed inside the residence 52 is higher than the set point on the thermostat, or the set point plus a small amount, the residential heating and cooling system 50 may become operative to refrigerate additional air for circulation through the residence 52. When the temperature reaches the set point, or the set point minus a small amount, the residential heating and cooling system 50 may stop the refrigeration cycle temporarily.

The residential heating and cooling system 50 may also operate as a heat pump. When operating as a heat pump, the roles of heat exchangers 60 and 62 are reversed. That is, the heat exchanger 60 of the outdoor unit 58 will serve as an evaporator to evaporate refrigerant and thereby cool air entering the outdoor unit 58 as the air passes over the outdoor heat exchanger 60. The indoor heat exchanger 62 will receive a stream of air blown over it and will heat the air by condensing the refrigerant.

In some embodiments, the indoor unit 56 may include a furnace system 70. For example, the indoor unit 56 may include the furnace system 70 when the residential heating and cooling system 50 is not configured to operate as a heat pump. The furnace system 70 may include a burner assembly and heat exchanger, among other components, inside the indoor unit 56. Fuel is provided to the burner assembly of the furnace 70 where it is mixed with air and combusted to form combustion products. The combustion products may pass through tubes or piping in a heat exchanger, separate from heat exchanger 62, such that air directed by the blower 66 passes over the tubes or pipes and extracts heat from the combustion products. The heated air may then be routed from the furnace system 70 to the ductwork 68 for heating the residence 52.

FIG. 4 is an embodiment of a vapor compression system 72 that can be used in any of the systems described above. The vapor compression system 72 may circulate a refrigerant through a circuit starting with a compressor 74. The circuit may also include a condenser 76, an expansion valve(s) or device(s) 78, and an evaporator 80. The vapor compression system 72 may further include a control panel 82 that has an analog to digital (A/D) converter 84, a microprocessor 86, a non-volatile memory 88, and/or an interface board 90. The control panel 82 and its components may function to regulate operation of the vapor compression system 72 based on feedback from an operator, from sensors of the vapor compression system 72 that detect operating conditions, and so forth.

In some embodiments, the vapor compression system 72 may use one or more of a variable speed drive (VSDs) 92, a motor 94, the compressor 74, the condenser 76, the expansion valve or device 78, and/or the evaporator 80. The motor 94 may drive the compressor 74 and may be powered by the variable speed drive (VSD) 92. The VSD 92 receives alternating current (AC) power having a particular fixed line voltage and fixed line frequency from an AC power source, and provides power having a variable voltage and frequency to the motor 94. In other embodiments, the motor 94 may be powered directly from an AC or direct current (DC) power source. The motor 94 may include any type of electric motor that can be powered by a VSD or directly from an AC or DC power source, such as a switched reluctance motor, an induction motor, an electronically commutated permanent magnet motor, or another suitable motor.

The compressor 74 compresses a refrigerant vapor and delivers the vapor to the condenser 76 through a discharge passage. In some embodiments, the compressor 74 may be a centrifugal compressor. The refrigerant vapor delivered by the compressor 74 to the condenser 76 may transfer heat to a fluid passing across the condenser 76, such as ambient or environmental air 96. The refrigerant vapor may condense to a refrigerant liquid in the condenser 76 as a result of thermal heat transfer with the environmental air 96. The liquid refrigerant from the condenser 76 may flow through the expansion device 78 to the evaporator 80.

The liquid refrigerant delivered to the evaporator 80 may absorb heat from another air stream, such as a supply air stream 98 provided to the building 10 or the residence 52. For example, the supply air stream 98 may include ambient or environmental air, return air from a building, or a combination of the two. The liquid refrigerant in the evaporator 80 may undergo a phase change from the liquid refrigerant to a refrigerant vapor. In this manner, the evaporator 80 may reduce the temperature of the supply air stream 98 via thermal heat transfer with the refrigerant. Thereafter, the vapor refrigerant exits the evaporator 80 and returns to the compressor 74 by a suction line to complete the cycle.

In some embodiments, the vapor compression system 72 may further include a reheat coil. In the illustrated embodiment, the reheat coil is represented as part of the evaporator 80. The reheat coil is positioned downstream of the evaporator heat exchanger relative to the supply air stream 98 and may reheat the supply air stream 98 when the supply air stream 98 is overcooled to remove humidity from the supply air stream 98 before the supply air stream 98 is directed to the building 10 or the residence 52.

It should be appreciated that any of the features described herein may be incorporated with the HVAC unit 12, the residential heating and cooling system 50, or other HVAC systems. Additionally, while the features disclosed herein are described in the context of embodiments that directly heat and cool a supply air stream provided to a building or other load, embodiments of the present disclosure may be applicable to other HVAC systems as well. For example, the features described herein may be applied to mechanical cooling systems, free cooling systems, chiller systems, or other heat pump or refrigeration applications.

As briefly discussed above, embodiments of the present disclosure are directed to a variable capacity furnace system configured to enable more efficient operation across a wider range of operating capacities of the HVAC system. To provide context for the following discussion, FIG. 5 is a schematic of an embodiment of a portion of an HVAC system 100 including a furnace 102 (e.g., furnace system, furnace system 70). The HVAC system 100 may include one or more components of the vapor compression system 72 discussed above and/or may be included in any of the systems described above (e.g., the HVAC unit 12, the heating and cooling system 50). The furnace 102 (e.g., furnace system, furnace system 70) is configured to operate to heat a supply air flow in a heating mode of the HVAC system 100. For example, the furnace 102 may be a portion of the indoor unit 56 discussed above. However, it should be appreciated that the techniques described herein may be incorporated in HVAC systems having other configurations, components, operating modes, and so forth.

The furnace 102 includes a housing 104 configured to contain or enclose one or more components of the furnace 102, such as a heat exchanger system 106 (e.g., heat exchange assembly) of the furnace 102. The heat exchanger system 106 is configured to enable transfer of thermal energy from a working fluid (e.g., combustion products) circulated through the heat exchanger system 106 and an air flow (e.g., a supply air flow) directed across the heat exchanger system 106. In some embodiments, the heat exchanger system 106 may be a condensing furnace system. To this end, the heat exchanger system 106 may include a first heat exchanger 108 (e.g., a primary heat exchanger) and a second heat exchanger 110 (e.g., a secondary heat exchanger). The working fluid generated by the furnace 102 may be directed sequentially through the first heat exchanger 108 and the second heat exchanger 110. That is, the working fluid (e.g., combustion products) may first be directed through the first heat exchanger 108 and thereafter may be directed through the second heat exchanger 110. Accordingly, the first heat exchanger 108 and the second heat exchanger 110 may be fluidly coupled to one another. Each of the first heat exchanger 108 and the second heat exchanger 110 may include one or more tubes or conduits (e.g., heat exchange tubes) configured to direct the working fluid therethrough. It should be appreciated that the tubes of the first heat exchanger 108 may be different in number, size, shape, material, and/or configuration than the tubes of the second heat exchanger 110, in some embodiments. Further, in some embodiments, the heat exchanger system 106 may include one heat exchanger (e.g., the first heat exchanger 108 or the second heat exchanger 110) instead of two heat exchangers.

To enable heat exchange between the working fluid circulated through the heat exchanger system 106 and an air flow, the furnace 102 includes a blower or fan 112 (e.g., a circulating fan), which may be disposed within the housing 104. The fan 112 may be driven in rotation by a motor 114. As the motor 114 drives rotation of the fan 112, the fan 112 draws or forces an air flow 116 (e.g., cool air flow) into the housing 104 via an inlet 118 of the housing 104. The air flow 116 may be any suitable air flow to be conditioned (e.g., heated) by the furnace 102, such as a return air flow, an outdoor (e.g., ambient) air flow, another air flow, or any combination thereof. In some embodiments, the furnace 102 include a filter 120 disposed within the housing 104 (e.g., adjacent the inlet 118) that is configured to filter or remove particles (e.g., dust, debris, chemical compounds, and so forth) from the air flow 116. Within the housing 104, the air flow 116 may be directed across the heat exchanger system 106 via operation of the fan 112. In the illustrated embodiment, the air flow 116 is first directed across the second heat exchanger 110 and is then directed across the first heat exchanger 108. As the air flow 116 flows across the first heat exchanger 108 and the second heat exchanger 110, the air flow 116 may contact respective tubes of the first heat exchanger 108 and the second heat exchanger 110. Accordingly, heat may be transferred via the tubes from the working fluid within the tubes to the air flow 116, thereby heating the air flow 116 to produce a supply air flow 122. The supply air flow 122 may then be discharged from the housing 104 via an outlet 124 of the housing 104. For example, the supply air flow 122 may be discharged into a duct of an air distribution system of a building or directly into a conditioned space serviced by the HVAC system 100.

As mentioned above, the furnace 102 is configured to generate a working fluid that is circulated through the heat exchanger system 106 (e.g., through respective tubes of the first heat exchanger 108 and the second heat exchanger 110). To this end, the furnace 102 includes one or more burners 126 (e.g., burner system, one or more burner assemblies) configured to generate the working fluid, such as combustion products. The burners 126 generate the combustion products by igniting an air-fuel mixture. Fuel (e.g., gas) may be supplied to the burners 126 via one or more fuel supply conduits 128 (e.g., piping). As described in further detail below, an amount (e.g., flow rate, mass flow rate) of fuel supplied to the burners 128 may be regulated by a fuel valve 130 (e.g., valve, modulating valve, control valve), which may be disposed along the fuel supply conduit 128. Although the illustrated embodiment includes one fuel valve 130, it should be appreciated that other embodiments may include multiple fuel valves 130. For example, the furnace 102 may include one fuel valve 130 associated with each burner 126 of the furnace 102.

A flow of air may be supplied to the burners 126 via a draft inducer blower 132 (e.g., draft inducer, draft inducing fan). In operation, the draft inducer blower 132 draws air into the one or more burners 126 for mixing with the fuel supplied to the burners 126. In some embodiments, the draft inducer blower 132 may be initially operated prior to operation of the fuel valve 130 to supply fuel to the burners 126, for example, to draw out any remaining combustion products within the tubes heat exchanger system 106 from a prior operating cycle of the furnace 102 and/or to ensure fresh air is provided to the burners 126 for mixing with the fuel.

The air and the fuel are mixed to form an air-fuel mixture, and the air-fuel mixture is ignited by the burners 126 to generate combustion products (e.g., working fluid). The combustion products are drawn through the respective tubes of the first heat exchanger 108 and the second heat exchanger 110 via operation of the draft inducer blower 132. After the combustion products circulate through the first heat exchanger 108 and the second heat exchanger 110, the draft inducer blower 132 may discharge the combustion products via a vent 134 (e.g., exhaust outlet) of the furnace 102. For example, the vent 134 may direct the exhausted combustion products to the atmosphere or other outdoor environment. The vent 134 may be formed from any suitable material, such as plastic, polyvinyl chloride (PVC), acrylonitrile butadiene styrene (ABS), or other suitable material.

As mentioned above, the furnace 102 may be a variable capacity furnace. In other words, the furnace 102 may be configured to operate at different operating capacities, such as to provide variable amounts of heat to the air flow 114. To enable operation at different operating capacities, operation of the fuel valve 130 and/or the draft inducer blower 132 may be adjusted. Specifically, the fuel valve 130 may be controlled to adjust an amount (e.g., mass flow rate) of fuel supplied to the burners 126. To this end, the fuel valve 130 may be a modulating valve or other suitable valve that is adjustable between a plurality of positions. As will be appreciated, a position of the fuel valve 130 may be expressed as a percentage by which a flow path through the fuel valve is open 130 (e.g., open percentage, percentage opening). For example, a position of the fuel valve 130 may be adjustable in 1 percent increments, such as 1 percent increments between 30 percent open (e.g., a lower threshold valve position) and 100 percent open (e.g., an upper threshold valve position). It should also be appreciated that a position of the fuel valve 130 and/or an open percentage of the fuel valve 130 may be described as a firing rate of the burners 126 and/or the furnace 102. Additionally or alternatively, variable capacity operation of the furnace 102 may be enabled via control of the draft inducer blower 132. For example, the draft inducer blower 132 may be a variable speed blower (e.g., driven by a variable speed motor). A speed of the draft inducer blower 132 may be adjusted to adjust an amount (e.g., mass flow rate) of air drawn into the burners 126 to mix with the fuel and create the air-fuel mixture ignited by the burners 126. Similarly, the speed of the draft inducer blower 132 may be adjusted to adjust a flow rate of the combustion products through the heat exchanger system 106. In this way, operation of the furnace 102 may be adjusted to enable operation at different operating capacities.

In accordance with presently disclosed techniques, the furnace 102 is configured to operate with variable air to fuel ratios of the air-fuel mixture produced and ignited by the furnace 102. The furnace 102 may be configured to determine a desired air to fuel ratio (e.g., a target air to fuel ratio) of the air-fuel mixture ignited by the burners 126 based on one or more operating parameters or conditions of the furnace 102. For example, the furnace 102 may determine a desired air to fuel ratio of the air-fuel mixture based on a firing rate (e.g., open percentage of the fuel valve 130, a target firing rate, target firing rate value, fuel value 130 position value). As discussed above, existing systems that utilize air-fuel mixtures with constant air to fuel ratios across a wide range of firing rates may operate inefficiently and/or unreliably. Accordingly, the present techniques enabling operation of the furnace 102 with air-fuel mixtures having different air to fuel ratios enable improved operation of the furnace 102 as compared to existing systems.

Based on the desired air to fuel ratio for a particular operating condition of the furnace 102, operation of the furnace 102 may be adjusted to achieve the desired air to fuel ratio. For example, operation of one or more components of the furnace 102 may be controlled to produce the air-fuel mixture with the desired air to fuel ratio for combustion via the burners 126. To this end, the furnace 102 further includes a furnace controller 136 (e.g., controller, control system) configured to control the furnace 102 and components of the furnace 102 in accordance with the techniques described herein. As discussed in further detail below, the furnace controller 136 may include processing circuitry configured to execute software for controlling the components of the furnace 102 and/or the HVAC system 100. The furnace controller 136 may also include a memory device (e.g., a memory) configured to store information, such as instructions, control software, executable-instructions, look up tables, data, and so forth.

The furnace controller 136 may be configured to control operation of the furnace 102 and components of the furnace 102 based on data and/or feedback received by the furnace controller 136. For example, the furnace controller 136 may be communicatively coupled to another controller of the HVAC system 100 (e.g., control board 48, control panel 82, a central controller) and/or to a control device (e.g., control device 16, mobile device), such as a thermostat 138. In some embodiments, the furnace controller 136 may additionally or alternatively be configured to receive data and/or feedback from one or more sensors 140 of the HVAC system 100. The one or more sensors 140 may be positioned within the housing 104, within another portion of the HVAC system 100, within a space conditioned by the HVAC system 100, and/or in another suitable locations. As an example, the one or more sensors 140 may include temperature sensors disposed within the conditioned space and configured to detect a temperature of air within the conditioned space, disposed within a return air duct (e.g., upstream of the inlet 118) and configured to detect a temperature of return air (e.g., air flow 116) received by the HVAC system 100, disposed within a supply air duct (e.g., downstream of the outlet 124) and configured to detect a temperature of supply air provided by the HVAC system 100, or a combination thereof.

In some embodiments, the furnace controller 136 may be configured to select and/or control an operating capacity of the furnace 102 based on the data and/or feedback received by the furnace controller 136, such as data indicative of an operating parameter of the furnace 102 and/or a parameter or characteristic of a space conditioned by the HVAC system 100. For example, the furnace controller 136 may operate the furnace 102 at a particular operating capacity based on a call for heating received from the thermostat 138. More specifically, the furnace controller 136 may operate the furnace 102 at a particular operating capacity based on a determined temperature differential between a set point temperature of the thermostat 138 (e.g., input by a user) and a detected temperature of a space conditioned by the HVAC system 100 (e.g., measured via one of the sensors 140). Based on the temperature differential (e.g., a magnitude of the temperature differential), the furnace controller 136 may operate the furnace 102 at a particular operating capacity, such as by controlling a firing rate (e.g., a position of the fuel valve 130) of the furnace 102. The furnace controller 136 may control operation of the furnace 102 based on other parameters, such as a temperature differential between a previous temperature of the conditioned space and a current temperature of the conditioned space, a deadband setting, an operating mode of the furnace 102, an ambient air temperature detected by one of the sensors 140, and so forth. Further, the furnace controller 136 may operate the furnace 102 produce the air-fuel mixture at variable air to fuel ratios. Operation of the furnace controller 136 to enable variable air to fuel ratios of the air-fuel mixture is described in further detail below.

While the illustrated embodiment includes the furnace controller 136 within the housing 104 of the furnace 102, it should be appreciated that the furnace controller 136 may be disposed in alternative locations and/or may be integrated with other controllers (e.g., of the HVAC system 100) in other embodiments. For example, the furnace controller 136 may be located external to the housing 104, may be a component of the control board 48 or control panel 82, may be separated into multiple controllers, and so forth.

FIG. 6 is a schematic of a portion of an embodiment of the furnace 102 of the HVAC system 100, illustrating the furnace controller 136 and components of the furnace controller 136. As discussed above, the furnace controller 136 is configured to regulate operation of the furnace 102 and components of the furnace 102 to heat the air flow 114 and produce the supply air flow 122. As discussed above, the furnace controller 136 may be communicatively coupled to one or more components of the HVAC system 100, such as the thermostat 138, the fuel valve 130, the draft inducer blower 132, and one or more sensors 140 associated with the HVAC system 100. For example, one or more control transfer devices, such as wires, cables, wireless communication devices, and the like, may communicatively couple the thermostat 138, the fuel valve 130, the draft inducer blower 132, the one or more sensors 140, and/or any other suitable components of the HVAC system 100 to the furnace controller 136. That is, the thermostat 138, the fuel valve 130, the draft inducer blower 132, the one or more sensors 140 may each have one or more communication components that facilitate wired or wireless (e.g., via a network) communication with the furnace controller 136. In some embodiments, the communication components may include a network interface that enables the components of the HVAC system 100 to communicate via various protocols such as EtherNet/IP, ControlNet, DeviceNet, or any other communication network protocol. Alternatively, the communication components may enable the components of the furnace 102 and/or HVAC system 100 to communicate via mobile telecommunications technology, Bluetooth®, near-field communications technology, and the like. As such, the furnace controller 136, the thermostat 138, the fuel valve 130, the draft inducer blower 132, and/or the one or more sensors 140 may wirelessly communicate data between each other.

The furnace controller 136 includes processing circuitry 150 with at least one processor 152, such as a microprocessor, which may execute software for controlling the components of the HVAC system 100. The processing circuitry 150 and/or the processor 152 may include multiple microprocessors, one or more “general-purpose” microprocessors, one or more special-purpose microprocessors, and/or one or more application specific integrated circuits (ASICS), or some combination thereof. For example, the processing circuitry 150 may include one or more reduced instruction set (RISC) processors.

The furnace controller 136 may also include a memory device 154 (e.g., a memory) configured to store information, such as instructions, control software, look up tables, data (e.g., configuration data), etc. The memory device 154 may include a volatile memory, such as random access memory (RAM), and/or a nonvolatile memory, such as read-only memory (ROM). The memory device 154 may store a variety of information and may be used for various purposes. For example, the memory device 154 may store processor-executable instructions including firmware or software for the processing circuitry 150 and/or the processor 152 to execute, such as instructions for controlling components of the HVAC system 100 and/or the furnace 102. In some embodiments, the memory device 154 is a tangible, non-transitory, machine-readable-medium that may store machine-readable instructions for the processing circuitry 150 (e.g., the processor 152) to execute. The memory device 154 may include ROM, flash memory, a hard drive, or any other suitable optical, magnetic, or solid-state storage medium, or a combination thereof. The memory device 154 may store data, instructions, and any other suitable data.

The furnace controller 136 is configured to operate the furnace 102 to heat the air flow 114 to produce the supply air flow 122 that is directed to a conditioned space. In accordance with present embodiments, the furnace controller 136 may be configured to determine and implement a desired operating capacity (e.g., target operating capacity) of the furnace 102. Indeed, the furnace 102 may be a variable capacity furnace configured to operate at each of a plurality of operating capacities. The furnace controller 136 may determine whether and how to operate the furnace 102 based on data received by one or more components of the HVAC system 100. For example, the thermostat 138 or other control device communicatively coupled to the furnace controller 136 may receive an input indicative of a desired temperature (e.g., set point temperature) of a space conditioned by the furnace 102, and data indicative of the set point temperature may be transmitted to the furnace controller 136. One or more of the sensors 140 (e.g., room air sensor, return air sensor) may detect and/or measure data indicative of a temperature within the conditioned space and may transmit the data to the furnace controller 136. In some embodiments, the furnace controller 136 may compare the set point temperature with the detected temperature to determine a temperature differential therebetween. In other embodiments, the thermostat 138 may receive the indicative of the temperature within the conditioned space may compare the set point temperature with the detected temperature to determine the temperature differential therebetween. In such embodiments, the thermostat 138 may transmit data indicative of the set point temperature, the temperature within the space, and/or temperature differential to the furnace controller 136.

In any case, the furnace controller 136 may be configured to determine a desired operation of the furnace 136, such as based on the set point temperature, the temperature within the conditioned space, the temperature differential therebetween, or a combination thereof. For example, in embodiments of the furnace 102 configured as a variable capacity furnace, the furnace controller 136 may determine a desired operating capacity at which to operate the furnace 102 based on various parameters, such as based on a magnitude of the temperature differential between the set point temperature and the detected temperature of the conditioned space (e.g., return air temperature). In other embodiments, the furnace controller 136 may determine a desired operating capacity of the furnace 102 based on a comparison of the set point temperature and a temperature of the supply air 122 discharged by the furnace 102, based on a comparison of the detected temperature of the conditioned space and the temperature of the supply air 122 discharged by the furnace 102, and/or based on other suitable parameters.

In some embodiments, the furnace controller 136 may implement the desired operating capacity of the furnace 102 by determining a desired firing rate (e.g., target firing rate, target firing rate value, target fuel valve 130 position value) of the furnace 102. In other words, the furnace controller 136 may determine an opening percentage of the fuel valve 130 of the furnace 102. To this end, the furnace controller 136 (e.g., the processing circuitry 150) may be configured to execute a control algorithm configured to determine a desired firing rate of the furnace 102 based on one or more of the parameters described herein. In some embodiments, the firing rate (e.g., fuel valve 130 position) may correlate with a magnitude of the temperature differential between the set point temperature and the detected temperature of the conditioned space (e.g., return air temperature). Data correlating the firing rate and the magnitude of the temperature differential may be stored in the memory device 154. Based on the desired firing rate (e.g., target firing rate) determined by the furnace controller 136, the furnace controller 136 may send instructions or control signals to the fuel valve 130 to adjust a position of the fuel valve 130 and achieve the desired firing rate. As mentioned above, in some embodiments, the firing rate of the furnace 102 may be between 30 percent and 100 percent. Additionally or alternatively, the desired firing rate may be determined based on a user input. In some embodiments, the furnace controller 136 may receive data or feedback from the fuel valve 130 indicative of a current firing rate at which the furnace 102 is operating, and the furnace controller 136 may utilize the current firing rate as a target firing rate to implement the present techniques.

As discussed above, the furnace controller 136 is also configured to determine a desired air to fuel ratio of the air-fuel mixture generated and ignited by the furnace 102 to produce the combustion products circulated through the heat exchanger system 106. Indeed, the furnace controller 136 may be configured to operate the furnace 102 to achieve different air to fuel ratios of the air-fuel mixture for different operating parameters or conditions of the furnace 102. For example, in some embodiments, the furnace controller 136 may operate the furnace 102 to achieve a particular air to fuel ratio of the air-fuel mixture based on a firing rate (e.g., fuel valve 130 position) of the furnace 102 that is determined by the furnace controller 136. As a result, the air to fuel ratio of the air-fuel mixture may be selected to enable more efficient and/or more reliable operation of the furnace 102. The furnace controller 136 may also select and/or adjust the air to fuel ratio of the air-fuel mixture based on other data and/or feedback. As an example, the furnace controller 136 may select or adjust an air to fuel ratio based on an indication of an unsuccessful ignition of one or more of the burners 126. In the manner described below, the furnace controller 136 is also configured to control the furnace 102 to achieve and/or maintain the desired air to fuel ratio of the air-fuel mixture.

In some embodiments, the memory device 154 includes a database 156 having data correlating various air to fuel ratios with various operating parameters of the furnace 102 and/or HVAC system 100. For example, the database 156 may include a lookup table 158 correlating different firing rates or fuel valve 130 positions (e.g., percentage values) of the furnace 102 with different air to fuel ratios (e.g., 13:1, 13.5:1, 14:1, etc.) of the air-fuel mixture. In some embodiments, each firing rate or fuel valve 130 position (e.g., 35 percent open, 36 percent open, 37 percent open, and so forth) may be separately associated with a respective air to fuel ratio. The data of the lookup table 158 may be determine utilizing any suitable technique. For example, the data of the lookup table 158 may be empirically determined and stored in the memory device 154. In another embodiment, the data of the lookup table 158 may be calculated using one or more equations (e.g., algebraic equations, polynomic equations). For example, the one or more equations may express an air to fuel ratio as a function of a firing rate of the furnace 102. The furnace controller 136 may be configured to execute the one or more equations to determine the data correlating air to fuel ratios with firing rates, or the one or more equations may be executed by another computing device and the resulting data may be stored in the database 156 (e.g., the lookup table 158). It should be appreciated that data correlating air to fuel ratios with firing rates of the furnace 102 may be stored in the database 156 in other formats. The database 156 may also store data correlating air to fuel ratios with other operating parameters of the furnace 102, such as temperature rises of the furnace 102 (e.g., a difference between supply air flow 122 temperature and air flow 114 or return air flow temperature), flame temperatures of the furnace 102, emissions characteristics of the furnace 102, and so forth.

Based on a particular firing rate of the furnace 102 determined by the furnace controller 136, the furnace controller 136 may determine a desired air to fuel ratio corresponding to the particular firing rate. To this end, the processing circuitry 150 (e.g., the memory device 154) of the furnace controller 136 includes a determination module 160. The determination module 160 is configured to determine or select the air to fuel ratio corresponding to the firing rate determined or selected by the furnace controller 136 (e.g., target firing rate). For example, the determination module 160 may receive the target firing rate and may reference the lookup table 158 stored in the database 156 to determine the particular air to fuel ratio corresponding to the target firing rate. In some embodiments, the determination module 160 may utilize a crawler and extractor (e.g., referencing data stored in the database 156) to determine the particular air to fuel ratio corresponding to the target firing rate. In other embodiments, the determination module 160 may configured to execute the one or more equations (e.g., stored in the database 156) discussed above utilizing a value indicative of the firing rate to determine the particular air to fuel ratio corresponding to the target firing rate.

Upon determining the particular air to fuel ratio corresponding to the target firing rate, the determination module 160 may determine an amount (e.g., mass flow rate) of fuel to be provided to the burners 126 (e.g., via the fuel valve 130) and/or an amount (e.g., mass flow rate) of air to be provided to the burners 126 (e.g., via the draft inducer blower 132) to achieve the particular air to fuel ratio of the air-fuel mixture. The determination module 160 may communicate the air to fuel ratio, the amount of fuel to be provided to the burners 126, and/or the amount of air to be provided to the burners 126 to an actuation module 162 of the furnace controller 136 (e.g., processing circuitry 150, memory device 154). The actuation module 162 is configured to control one or more components of the furnace 102 to achieve the particular air to fuel ratio determined by the determination module 160. For example, the actuation module 162 may generate and send control signals (e.g., pulse width modulation [PWM] signals) to the fuel valve 130 to cause the fuel valve 130 to provide the amount of fuel to the burners 126 that enables generation of the air-fuel mixture at the particular air to fuel ratio. Similarly, the actuation module 162 may generate and send control signals (e.g., PWM signals) to the draft inducer blower 132 to cause the draft inducer blower 132 to provide the amount of air to the burners 126 that enables generation of the air-fuel mixture at the particular air to fuel ratio. In some embodiments, the draft inducer blower 132 may include a controller 164 (e.g., dedicated controller, separate controller, integrated controller, air flow controller) configured to regulate operation of the draft inducer blower 132 (e.g., a motor of the draft inducer lower 132). In such embodiments, the actuation module 162 may generate and send control signals (e.g., PWM signals) to the controller 164 of the draft inducer blower 132, and the controller 164 may control operation of the draft inducer blower 132 to provide the amount of air to the burners 126 associated with the particular air to fuel ratio. In accordance with present techniques, the actuation module 162 (e.g., the furnace controller 136) may control and/or adjust operation of the fuel valve 130, the draft inducer blower 132, or both to achieve and/or maintain the particular air to fuel ratio associated with the firing rate and/or operating capacity of the furnace 102.

In some embodiments, one or more of the sensors 140 may be positioned and configured to detect an operating parameter associated with the fuel and/or the air supplied to the burners 126 and may provide feedback to the furnace controller 136 indicative of the operating parameter. The feedback may be analyzed by the controller 136 to evaluate and/or verify the air to fuel ratio achieved by the furnace 102. For example, the one or more sensors 140 may be configured to detect a flow rate of the fuel directed through the fuel supply conduits 128, a position of the fuel vale 130, a speed of the draft inducer blower 132, a pressure and/or flow rate of air drawn into the furnace 102 by the draft inducer blower 132, a pressure and/or flow rate of combustion products discharged from the furnace 102 via the vent 134, another suitable operating parameter, or any combination thereof.

The lookup table 158 stored on the database 156 may be associated with a particular embodiment of the furnace 102 and/or HVAC system 100. More particularly, the lookup table 158 may store data, such as various air to fuel ratios corresponding to various operating parameters (e.g., firing rates) of the particular embodiment of the furnace 102 and/or HVAC system 100. For example, the lookup table 158 may store data particular to a type of the furnace 102, a model of the furnace 102, a rated capacity of the furnace 102, a configuration of the furnace 102, a type or configuration of the heat exchanger assembly 106, particular operating characteristics or parameters of the furnace 102, other characteristics of the furnace 102, or any combination thereof. In addition, the database 156 may also include additional lookup tables 166 stored thereon. In some embodiments, the additional lookup tables 166 may be associated with other embodiments of the furnace 102, such as different models of the furnace 102. As a result, the furnace controller 136 (e.g., the same embodiment of the furnace controller 136) may be configured for implementation with different embodiments of the furnace 102. The furnace controller 136 may therefore be configured to reference a particular lookup table (e.g., lookup table 158, one of the additional lookup tables 166) based on an identification of the furnace 102 with which the furnace controller 136 is implemented. For example, the furnace controller 136 may reference a particular lookup table stored on the database 156 based on a determined model (e.g., model identification number or code), capacity, design, implementation, and/or other characteristic of the furnace 102. In this way, the furnace controller 136 may be readily implemented with multiple types of furnaces 102, which may reduce costs associated with manufacture of the furnace 102 and HVAC system 100.

The furnace controller 136 may also be configured to receive and store updated information in the database 156. To this end, the furnace controller 136 may include communications circuitry 168 configured to receive and/or transmit communications, such as data, feedback, control signals, and/or other suitable information. As an example, an embodiment of the furnace 102 having the furnace controller 136 with the database 156 and lookup table 158 stored on the memory device 154 may be manufactured and installed in a particular location or application. Thereafter, additional, updated, and/or improved data for the lookup table 158 (e.g., data correlating various air to fuel ratios with respective operating parameter values, such as firing rates or valve position, of the furnace 102) may be developed. The new data (e.g., an updated lookup table) may be readily uploaded to the furnace controller 136 and stored in the memory device 154 (e.g., the database 156) via the communications circuitry 168. In some embodiments, the furnace controller 136 may include an input port communicatively coupled to the communications circuitry, and the furnace controller 136 may receive the new data via a hardwired connection to the input port. Additionally or alternatively, the communications circuitry 168 may be configured to send and/or receive wireless communications, such as via any of the protocols described above. Thus, the furnace controller 136 may receive new data via an over-the-air (OTA) update from a system or device that is remote from the furnace controller 136 (e.g., a mobile device, a cloud server, an internet connection, and so forth). In this way, the furnace controller 136 may be readily updated to provide improved selections and implementations of variable air to fuel ratios for operation of the furnace 102.

In the manner described above, present embodiments enable improved operation of the HVAC system by improving operation of a furnace of the HVAC system. Specifically, embodiments of the present disclosure are directed to furnace systems configured to operate with variable air to fuel ratios for an air-fuel mixture generated and ignited by the furnace system. For example, a furnace system is configured to determine a desired air to fuel ratio based on a determined operating parameter of the furnace system. The operating parameter may be a firing rate (e.g., fuel valve position) or any other suitable operating parameter value at which the furnace system may be operated. Each operating parameter value may be associated with a respective, corresponding air to fuel ratio. Based on a determined air to fuel ratio for a particular operating parameter of the furnace system, the furnace system may be operated to achieve the desired air to fuel ratio. In this way, furnace systems incorporating the present techniques may operate more efficiently and more reliably across a wider range of firing rates (e.g., valve positions, operating capacities). Indeed, embodiments incorporating the present techniques may enable operation of variable capacity furnace systems with reduced emissions, improved efficiency, and reduced costs.

While only certain features and embodiments have been illustrated and described, many modifications and changes may occur to those skilled in the art, such as variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, such as temperatures and pressures, mounting arrangements, use of materials, colors, orientations, and so forth, without materially departing from the novel teachings and advantages of the subject matter recited in the claims. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the disclosure.

Furthermore, in an effort to provide a concise description of the exemplary embodiments, all features of an actual implementation may not have been described, such as those unrelated to the presently contemplated best mode, or those unrelated to enablement. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation specific decisions may be made. Such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure, without undue experimentation.

The techniques presented and claimed herein are referenced and applied to material objects and concrete examples of a practical nature that demonstrably improve the present technical field and, as such, are not abstract, intangible or purely theoretical. Further, if any claims appended to the end of this specification contain one or more elements designated as “means for [perform]ing [a function] . . . ” or “step for [perform]ing [a function] . . . ”, it is intended that such elements are to be interpreted under 35 U.S.C. 112(f). However, for any claims containing elements designated in any other manner, it is intended that such elements are not to be interpreted under 35 U.S.C. 112(f). 

1. A furnace for a heating, ventilation, and air conditioning (HVAC) system, comprising: a fuel valve configured to regulate an amount of fuel supplied to a burner of the furnace; a draft inducer blower configured to draw an air flow into the burner; and a controller configured to: determine a target operating parameter value of the furnace; determine an air to fuel ratio corresponding to the target operating parameter value; and control operation of the fuel valve, the draft inducer blower, or both based on the air to fuel ratio.
 2. The furnace of claim 1, wherein the controller comprises a memory device, and the air to fuel ratio and the target operating parameter value are stored on the memory device.
 3. The furnace of claim 2, wherein the memory device comprises: a plurality of air to fuel ratios including the air to fuel ratio stored on the memory device; and a plurality of target operating parameter values including the target operating parameter value stored on the memory device, wherein each target operating parameter value of the plurality of target operating parameter values corresponds to a respective air to fuel ratio of the plurality of air to fuel ratios.
 4. The furnace of claim 3, wherein the memory device comprises a lookup table stored thereon, and the lookup table associates each target operating parameter value of the plurality of target operating parameter values with the respective air to fuel ratio of the plurality of air to fuel ratios.
 5. The furnace of claim 1, wherein the target operating parameter value corresponds to a firing rate of the furnace.
 6. The furnace of claim 5, wherein the target operating parameter value comprises a value indicative of a position of the fuel valve.
 7. The furnace of claim 1, wherein the controller comprises a memory device, the memory device comprises a lookup table stored thereon, the lookup table comprises a plurality of target operating parameter values including the target operating parameter value and a plurality of air to fuel ratios including the air to fuel ratio, and each target operating parameter value of the plurality of target operating parameter values corresponds to at least one air to fuel ratio of the plurality of air to fuel ratios.
 8. The furnace of claim 7, wherein the lookup table is a first lookup table, the memory device comprises an additional lookup table stored thereon, the additional lookup table comprises a plurality of additional target operating parameter values and a plurality of additional air to fuel ratios, each additional target operating parameter value of the plurality of additional target operating parameter values corresponds to at least one additional air to fuel ratio of the plurality of additional air to fuel ratios, and the additional lookup table is associated with an additional furnace different from the furnace.
 9. The furnace of claim 8, wherein the furnace and the additional furnace comprise different configurations, different models, different components, different operating capacities, or any combination thereof.
 10. The furnace of claim 9, wherein the controller is configured to: receive an identification of the furnace; and reference the lookup table to determine the air to fuel ratio corresponding to the target operating parameter value based on the identification of the furnace.
 11. A furnace controller for a furnace of a heating, ventilation, and air conditioning (HVAC) system, comprising: processing circuitry; and a memory, wherein the memory comprises instructions that, when executed by the processing circuitry, cause the processing circuitry to: determine a target firing rate of the furnace; determine an air to fuel ratio of a plurality of air to fuel ratios corresponding to the target firing rate; and control operation of a fuel valve of the furnace, a draft inducer blower of the furnace, or both based on the air to fuel ratio.
 12. The furnace controller of claim 11, wherein the memory comprises a database, the database comprises the plurality of air to fuel ratios and a plurality of target firing rates including the target firing rate, and each target firing rate of the plurality of target firing rates is associated with at least one air to fuel ratio of the plurality of air to fuel ratios in the database.
 13. The furnace controller of claim 11, wherein the target firing rate corresponds to a position of the fuel valve.
 14. The furnace controller of claim 11, wherein the instructions, when executed by the processing circuitry, cause the processing circuitry to: receive data indicative of a temperature within a conditioned space from a sensor; receive data indicative of a set point temperature of the conditioned space; and determine the target firing rate based on the temperature within the conditioned space, the set point temperature of the conditioned space, or both.
 15. The furnace controller of claim 14, wherein the instructions, when executed by the processing circuitry, cause the processing circuitry to: determine a temperature differential between the temperature within the conditioned space and the set point temperature of the conditioned space; and determine the target firing rate based on the temperature differential.
 16. The furnace controller of claim 11, wherein the instructions, when executed by the processing circuitry, cause the processing circuitry to: adjust a position of the fuel valve based on the target firing rate; and control operation of the draft inducer blower of the furnace based on the air to fuel ratio.
 17. A furnace for a heating, ventilation, and air conditioning (HVAC) system, comprising: a burner configured to receive a flow of fuel and an air flow, to mix the flow of fuel and the air flow produce an air-fuel mixture, and to ignite the air-fuel mixture to generate combustion products; a heat exchanger system configured to receive the combustion products and direct the combustion products therethrough; and a controller comprising a memory, wherein the controller configured to: determine a target operating parameter value of the furnace based on data received by the controller; select an air to fuel ratio of a plurality of air to fuel ratios stored on the memory, wherein the air to fuel ratio corresponds to the target operating parameter value; and control operation of the furnace to produce the air-fuel mixture with the air to fuel ratio.
 18. The furnace of claim 17, comprising: a fuel valve configured to regulate the flow of fuel directed to the burner; and a draft inducer blower configured to draw the air flow into the burner and to draw the combustion products through the heat exchanger system, wherein the controller is configured to control operation of the fuel valve, the draft inducer blower, or both to produce the air-fuel mixture with the air to fuel ratio.
 19. The furnace of claim 18, wherein the target operating parameter value corresponds to a position of the fuel valve, the data comprises a measured temperature indicative of a current temperature of a conditioned space associated with the furnace and comprises a set point temperature of the conditioned space, and the controller is configured to determine the target operating parameter value based on a temperature differential between the measured temperature and the set point temperature.
 20. The furnace of claim 17, wherein: the memory comprises a lookup table, the lookup table comprises the plurality of air to fuel ratios and a plurality of target operating parameter values including the target operating parameter value, each target operating parameter value of the plurality of target operating parameter values is associated with at least one air to fuel ratio of the plurality of air to fuel ratios in the lookup table, and the controller is configured to reference the lookup table to select the air to fuel ratio corresponding to the target operating parameter value. 